Mountain glaciation drives rapid oxidation of rock-bound organic carbon

Horan, Kate; Hilton, Robert; Selby, David; Ottley, Chris J.; Gröcke, Darren R.; Hicks, Murray; Burton, Kevin W.

doi:10.1126/sciadv.1701107

Cited by 65 publications

(105 citation statements)

References 64 publications

(214 reference statements)

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“…CO 2 fluxes derived from the oxidation of rock organic carbon have been indirectly estimated using geochemical proxies, such as dissolved rhenium fluxes in rivers (Dalai et al, 2002;Hilton et al, 2014;Horan et al, 2017). Our direct measurements obtained from a single chamber (H6) (62 ± 2 gC m −2 yr −1 ) are of the same order of magnitude as that calculated in highly erosive Taiwanese catchments using dissolved rhenium yields and the loss of rock organic carbon from soils (5 to 35 gC m −2 yr −1 ) (Hilton et al, 2014;Hemingway et al, 2018).…”

Section: Rock-derived Organic Carbon Oxidationmentioning

confidence: 99%

“…These include the use of geochemical proxies in rivers, which indirectly track the CO 2 emissions from the oxidative weathering of sedimentary rocks at the catchment scale. For instance, the trace element rhenium has been used to compare relative rates of rock-derived organic carbon oxidation (Jaffe et al, 2002) and estimate the corresponding fluxes of CO 2 across river catchments (Dalai et al, 2002;Hilton et al, 2014;Horan et al, 2017). Another approach has been to measure the loss of radiocarbon-depleted organic matter in river sediments during their transfer across the floodplains of large river basins (Bouchez et al, 2010;Galy et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Technical note: In situ measurement of flux and isotopic composition of CO2 released during oxidative weathering of sedimentary rocks

et al. 2018

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Abstract. Oxidative weathering of sedimentary rocks can release carbon dioxide (CO 2 ) to the atmosphere and is an important natural CO 2 emission. Two mechanisms operatethe oxidation of sedimentary organic matter and the dissolution of carbonate minerals by sulfuric acid. It has proved difficult to directly measure the rates at which CO 2 is emitted in response to these weathering processes in the field, with previous work generally using methods which track the dissolved products of these reactions in rivers. Here we design a chamber method to measure CO 2 production during the oxidative weathering of shale bedrock, which can be applied in erosive environments where rocks are exposed frequently to the atmosphere. The chamber is drilled directly into the rock face and has a high surface-area-tovolume ratio which benefits measurement of CO 2 fluxes. It is a relatively low-cost method and provides a long-lived chamber (several months or more). To partition the measured CO 2 fluxes and the source of CO 2 , we use zeolite molecular sieves to trap CO 2 "actively" (over several hours) or "passively" (over a period of months). The approaches produce comparable results, with the trapped CO 2 having a radiocarbon activity (fraction modern, Fm) ranging from Fm = 0.05 to Fm = 0.06 and demonstrating relatively little contamination from local atmospheric CO 2 (Fm = 1.01). We use stable carbon isotopes of the trapped CO 2 to partition between an organic and inorganic carbon source. The measured fluxes of rock-derived organic matter oxidation (171 ± 5 mgC m −2 day −1 ) and carbonate dissolution by sulfuric acid (534 ± 16 mgC m −2 day −1 ) from a single chamber were high when compared to the annual flux estimates derived from using dissolved river chemistry in rivers around the world. The high oxidative weathering fluxes are consistent with the high erosion rate of the study region. We propose that our in situ method has the potential to be more widely deployed to directly measure CO 2 fluxes during the oxidative weathering of sedimentary rocks, allowing for the spatial and temporal variability in these fluxes to be determined.

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Section: Rock-derived Organic Carbon Oxidationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Technical note: In situ measurement of flux and isotopic composition of CO2 released during oxidative weathering of sedimentary rocks

et al. 2018

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“…This might be 25 explained by the much lower erosion rates of the Canadian site, with deep soils and stable geomorphology, compared to the Laval catchment where erosion continuously exposes rocks to oxidative weathering (Graz et al, 2012). CO2 fluxes derived from the oxidation rock organic carbon have been indirectly estimated using geochemical proxies, such as dissolved rhenium fluxes in rivers (Dalai et al, 2002;Hilton et al, 2014;Horan et al, 2017). Our direct measurements obtained from a single chamber (H6) (66 ± 2 gC.m and that CO2 fluxes from a single chamber may vary throughout the year.…”

Section: Rock-derived Organic Carbon Oxidationmentioning

confidence: 99%

“…For instance, the trace element rhenium has been used to compare relative rates of rock-derived organic carbon oxidation (Jaffe et al, 2002) and estimate the corresponding fluxes of CO2 across river catchments (Dalai et al, 2002;20 Hilton et al, 2014;Horan et al, 2017). Another approach has been to measure the loss of radiocarbon-depleted organic matter in river sediments during their transfer across the floodplains of large river basins (Bouchez et al, 2010;Galy et al, 2008).…”

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confidence: 99%

Technical note: in situ measurement of flux and isotopic composition of CO2 released during oxidative weathering of sedimentary rocks

Soulet¹,

Hilton²,

Garnett³

et al. 2017

Preprint

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Abstract. Oxidative weathering of sedimentary rocks can release carbon dioxide (CO2) to the atmosphere and is an important natural CO2 emission. Two mechanisms operate -the oxidation of sedimentary organic matter and the dissolution of carbonate 10 minerals by sulphuric acid. It has proved difficult to directly measure the rates of these weathering processes in the field, with previous work generally using indirect methods which track the dissolved products of these reactions in rivers. Here we design a chamber method to measure CO2 production during the oxidative weathering of shale bedrock, which can be applied in erosive environments where rocks are exposed frequently to the atmosphere. The chamber is drilled directly into the rock face and is a relatively low cost method to provide a long-lived (several months or more), oxygenated environment in contact with 15 a surface area of potential reactant. To partition the measured CO2 fluxes and the source of CO2, we use zeolite molecular sieves to trap CO2 'actively' (over several hours) or 'passively' (over a period of months). The approaches produce comparable results, with the trapped CO2 having a fraction modern ranging from 0.05 to 0.06 and demonstrating relatively little contamination from local atmospheric CO2 (fraction modern of 1.01). We use stable isotopes of the trapped CO2 to partition between an organic and inorganic carbon source. The measured fluxes of rock-derived organic matter oxidation and carbonate 20 dissolution by sulphuric acid from a single chamber were high, but consistent with the high erosion rate of the study region (of ~5 mm yr -1 ). We propose our in situ method has the potential to be more widely deployed to directly measure CO2 fluxes during the oxidative weathering of sedimentary rocks, allowing for the spatial and temporal variability in these fluxes to be determined.

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“…The last is meant to represent a generalized period of elevated overall surface erosion/weathering rates, as is likely to have occurred many times throughout Earth's geologic history. Indeed, petrogenic organic carbon oxidation appears to be enhanced in some rapidly eroding regions of Earth's surface (Horan et al, 2017), suggesting that in some regions weathering rates of all the dominant crustal phases considered in our model will rise and fall in parallel.…”

Section: Geochemistry Geophysics Geosystemsmentioning

confidence: 96%

Mechanistic Links Between the Sedimentary Redox Cycle and Marine Acid‐Base Chemistry

Reinhard

Fischer

2019

Geochem Geophys Geosyst

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The redox state of Earth's surface is controlled on geological timescales by the flow of electrons through the sedimentary rock cycle, mediated largely by the weathering and burial of C-S-Fe phases. These processes buffer atmospheric pO 2 . At the same time, CO 2 influxes and carbonate burial control seawater acid-base chemistry and climate over long timescales via the carbonate-silicate cycle. However, these two systems are mechanistically linked and impact each other via charge balance in the hydrosphere. Here, we use a low-order Earth system model to interrogate a subset of these connections, with a focus on changes that occur during perturbations to electron flow through the sedimentary rock cycle. We show that the net oxidation or reduction of the Earth's surface can play an important role in controlling acid-base processes in the oceans and thus climate, and suggest that these links should be more fully integrated into interpretive frameworks aimed at understanding Earth system evolution throughout Precambrian and Phanerozoic time.

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Mountain glaciation drives rapid oxidation of rock-bound organic carbon

Abstract: Mountain glaciation greatly enhances oxidative weathering rates of organic carbon in rocks and associated carbon dioxide release.

Cited by 65 publications

References 64 publications

Technical note: In situ measurement of flux and isotopic composition of CO<sub>2</sub> released during oxidative weathering of sedimentary rocks

Technical note: In situ measurement of flux and isotopic composition of CO<sub>2</sub> released during oxidative weathering of sedimentary rocks

Technical note: in situ measurement of flux and isotopic composition of CO<sub>2</sub> released during oxidative weathering of sedimentary rocks

Mechanistic Links Between the Sedimentary Redox Cycle and Marine Acid‐Base Chemistry

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Mountain glaciation drives rapid oxidation of rock-bound organic carbon

Abstract: Mountain glaciation greatly enhances oxidative weathering rates of organic carbon in rocks and associated carbon dioxide release.

Cited by 65 publications

References 64 publications

Technical note: In situ measurement of flux and isotopic composition of CO&lt;sub&gt;2&lt;/sub&gt; released during oxidative weathering of sedimentary rocks

Technical note: In situ measurement of flux and isotopic composition of CO&lt;sub&gt;2&lt;/sub&gt; released during oxidative weathering of sedimentary rocks

Technical note: in situ measurement of flux and isotopic composition of CO&lt;sub&gt;2&lt;/sub&gt; released during oxidative weathering of sedimentary rocks

Mechanistic Links Between the Sedimentary Redox Cycle and Marine Acid‐Base Chemistry

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Product

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Technical note: In situ measurement of flux and isotopic composition of CO<sub>2</sub> released during oxidative weathering of sedimentary rocks

Technical note: In situ measurement of flux and isotopic composition of CO<sub>2</sub> released during oxidative weathering of sedimentary rocks

Technical note: in situ measurement of flux and isotopic composition of CO<sub>2</sub> released during oxidative weathering of sedimentary rocks